IN TERPRETATION AND QUALIFICATION. 477 



as the other. This absence of difference cannot be ascribed 

 to their unlike degrees of activity. "We must seek its cause in 

 some facility of living secured to the Rat by its greater intel- 

 ligence, greater power and courage, greater ability to utilize 

 what it finds. The Rat is notoriously cunning ; and its 

 cunning gives success to its foraging expeditions. It is not, 

 like the Mouse, limited mainly to vegetal food ; but while it 

 eats grain and beans like the Mouse, it also eats flesh and 

 carrion, devours young poultry and eggs. The result is that, 

 without a proportionate increase of expenditure, it gets a far 

 larger supply of nourishment than the Mouse ; and this rela- 

 tive excess of nourishment makes possible a large size without 

 a smaller rate of multiplication. How clearly this is the 

 cause, we see in the contrast between the common Rat and 

 the Water-Rat. While the common Rat has habitually 

 several broods a-year of from 10 to 12 each, the Water-Rat, 

 though somewhat smaller, has but 5 or 6 in a brood, and but 

 one brood, or sometimes two broods, a-year. But the Water- 

 Rat lives on vegetal food — lacks all that its bold, sagacious, 

 omnivorous congener, gains from the warmth as well as the 

 abundance which men's habitations yield. 



The inverse variation of Individuation and Genesis is, 

 therefore, but approximate. Recognizing the truth that 

 every increment of evolution which is appropriate to the 

 circumstances of an organism, brings an advantage somewhat 

 in excess of its cost ; we see the general law, as more strictly 

 stated, to be that Genesis decreases not quite so fast as In- 

 dividuation increases. Whether the greater Individuation 

 takes the form of a larger bulk and accompanying access of 

 strength ; whether it be shown in higher speed or agility ; 

 whether it consists in a modification of structure that 

 facilitates some habitual movement, or in a visceral change 

 that helps to utilize better the absorbed aliment ; the ultimate 

 effect is identical. There is either a more economical per- 

 formance of the same actions, internal or external, or there 

 is a securing of greater advantages by modified actions, which 



